You got to love some people. It seems that the Shroud of Turin was not painted by Leonardo da Vinci, as many have maintained, but by Giotto, or at least this is what one Italian artist wants us to believe. This theory will get the same response as the "Da Vinci" one. As far as the most up to date scientific techniques can discern there is no paint on the Shroud, and the image was produced by some sort of process which is still unknown to us, though similiar to photography. So far, though, the most up to date photographic techniques have failed to reproduce the Shroud exactly.
Of course we will never convince those who do not believe (or will not believe). My own personal opinion is that it is genuine and science is gradually edging towards that conclusion. In reality there is more scientific and historical evidence in favour of authenticity than it being a medieval fake. The Shroud's critics, of course, tend to pick and choose the evidence they want to acknowledge. The Carbon-14 test is still being resurrected (no pun intended) long after sindonologists have left it behind and moved on, recognising that it is no longer reliable.
But you have to hand it to the critics they are still working hard; many of them cannot bring themselves to accept it - to do so would mean they would have to accept much more than they want to. The more the Shroud is investigated, the more of an enigma it becomes, the more mysterious and more complex. The more they know about it, the more they realise they know so little. I think there is a sign in that.
Interestingly, the whole field of study which has developed around the Shroud - sindonology, has done a great deal to bring science and religion together. In this unique area of research numerous disciplines work together to unravel this scientific and historical tapesty, or what has been called, an icon of the suffering Christ.